ACPI / battery: introduce support for POWER_SUPPLY_PROP_CAPACITY_LEVEL

ACPI battery device receives notifications when
1. the remaining battery capacity becomes critical low
2. the trip point set by the _BTP (Design capacity of Warning by default)
   is reached or crossed.

So it is able to support POWER_SUPPLY_PROP_CAPACITY_LEVEL to report
        POWER_SUPPLY_CAPACITY_LEVEL_CRITICAL,
        POWER_SUPPLY_CAPACITY_LEVEL_LOW,
        POWER_SUPPLY_CAPACITY_LEVEL_NORMAL,
        POWER_SUPPLY_CAPACITY_LEVEL_FULL,
capacity levels to power supply core and user space.

Introduce support for POWER_SUPPLY_PROP_CAPACITY_LEVEL in this patch.
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/battery.c

@@ -56,6 +56,10 @@
 /* Battery power unit: 0 means mW, 1 means mA */
 #define ACPI_BATTERY_POWER_UNIT_MA	1
 
+#define ACPI_BATTERY_STATE_DISCHARGING	0x1
+#define ACPI_BATTERY_STATE_CHARGING	0x2
+#define ACPI_BATTERY_STATE_CRITICAL	0x4
+
 #define _COMPONENT		ACPI_BATTERY_COMPONENT
 
 ACPI_MODULE_NAME("battery");
@@ -169,7 +173,7 @@ static int acpi_battery_get_state(struct acpi_battery *battery);
 
 static int acpi_battery_is_charged(struct acpi_battery *battery)
 {
-	/* either charging or discharging */
+	/* charging, discharging or critical low */
 	if (battery->state != 0)
 		return 0;
 
@@ -204,9 +208,9 @@ static int acpi_battery_get_property(struct power_supply *psy,
 		return -ENODEV;
 	switch (psp) {
 	case POWER_SUPPLY_PROP_STATUS:
-		if (battery->state & 0x01)
+		if (battery->state & ACPI_BATTERY_STATE_DISCHARGING)
 			val->intval = POWER_SUPPLY_STATUS_DISCHARGING;
-		else if (battery->state & 0x02)
+		else if (battery->state & ACPI_BATTERY_STATE_CHARGING)
 			val->intval = POWER_SUPPLY_STATUS_CHARGING;
 		else if (acpi_battery_is_charged(battery))
 			val->intval = POWER_SUPPLY_STATUS_FULL;
@@ -269,6 +273,17 @@ static int acpi_battery_get_property(struct power_supply *psy,
 		else
 			val->intval = 0;
 		break;
+	case POWER_SUPPLY_PROP_CAPACITY_LEVEL:
+		if (battery->state & ACPI_BATTERY_STATE_CRITICAL)
+			val->intval = POWER_SUPPLY_CAPACITY_LEVEL_CRITICAL;
+		else if (test_bit(ACPI_BATTERY_ALARM_PRESENT, &battery->flags) &&
+			(battery->capacity_now <= battery->alarm))
+			val->intval = POWER_SUPPLY_CAPACITY_LEVEL_LOW;
+		else if (acpi_battery_is_charged(battery))
+			val->intval = POWER_SUPPLY_CAPACITY_LEVEL_FULL;
+		else
+			val->intval = POWER_SUPPLY_CAPACITY_LEVEL_NORMAL;
+		break;
 	case POWER_SUPPLY_PROP_MODEL_NAME:
 		val->strval = battery->model_number;
 		break;
@@ -296,6 +311,7 @@ static enum power_supply_property charge_battery_props[] = {
 	POWER_SUPPLY_PROP_CHARGE_FULL,
 	POWER_SUPPLY_PROP_CHARGE_NOW,
 	POWER_SUPPLY_PROP_CAPACITY,
+	POWER_SUPPLY_PROP_CAPACITY_LEVEL,
 	POWER_SUPPLY_PROP_MODEL_NAME,
 	POWER_SUPPLY_PROP_MANUFACTURER,
 	POWER_SUPPLY_PROP_SERIAL_NUMBER,
@@ -313,6 +329,7 @@ static enum power_supply_property energy_battery_props[] = {
 	POWER_SUPPLY_PROP_ENERGY_FULL,
 	POWER_SUPPLY_PROP_ENERGY_NOW,
 	POWER_SUPPLY_PROP_CAPACITY,
+	POWER_SUPPLY_PROP_CAPACITY_LEVEL,
 	POWER_SUPPLY_PROP_MODEL_NAME,
 	POWER_SUPPLY_PROP_MANUFACTURER,
 	POWER_SUPPLY_PROP_SERIAL_NUMBER,